The present invention relates generally to wireless local area networks (WLAN) and in particular to a method and system for pre-authenticating a wireless station on a different subnet.
The Institute of Electrical and Electronics Engineers (IEEE) 802.11i standard for Medium Access Control (MAC) Security enhancements includes an optional phase for wireless station pre-authentication. Pre-authentication is designed to allow a supplicant to establish security associations with multiple access points (AP) preceding a direct association to those APs in order to improve the performance of fast (re)-association in a mobile environment. Pre-authentication can be a useful performance enhancement, as now roaming associations will not include the full protocol overhead of a full re-authentication of the supplicant.
Per the 802.11i standard, pre-authentication uses the IEEE 802.1X protocol and state machines with EtherType 88-C7. To effect pre-authentication, the wireless station's (STA's) Supplicant sends an IEEE 802.1X EAPOL-Start (Extensible Authentication Protocol Over Lan) message with the Destination Address (DA) being the Basic Service Set Identification (BSSID) of the targeted AP and the Return Address (RA) being the BSSID of the AP with which the Supplicant is associated. The target AP uses a BSSID equal to the radio MAC address of its authenticator.
In order to generate these pre-authentication requests, a mobile node (MN) or wireless station (STA) will use the radio MAC address of the potential APs that the MN may roam to, as the identifier of APs for pre-authentication. A problem with this approach is that there may exist situations where there are APs that a supplicant can pre-authenticate to that are not in the same subnet. Thus, although the pre-authentication standard allows for supplicants to pre-authenticate to all access points they can “see” (receive beacons from), the access point and/or infrastructure that is associated with that station may not know how to locate, find, or route to access point radio MAC address(es) that are not in the same local subnet. Thus, the need exists for a method for enabling supplicants to pre-authenticate with access points, or other infrastructure nodes that are on different subnets.